Similar, though funnier (peculiarwise) story on our MCO-ATL-NRT-PEK outbound and return HKG-NRT-ATL-MCO late last year. All on DL/NW.

Was a pair of J award tickets "purchased" 8 months earlier. There were the usual schedule changes, flight adjustments, and so on.

Boarded at MCO fine. In the ATL Sky Club we were informed there was an "inconsistency" with our ticket and to have the gate agent in NRT handle it. At NRT I was told it was only a "reissue" situation and they would take care of it but meanwhile here's your boarding pass and have a nice flight.

Fast forward to check in at HKG. Passports check, bags tagged and sent down the conveyor check, boarding passes...oops. Was told to step aside for a few minutes. Long story short, 45 minutes later we had the BPs and were told the tickets had never been reissued. In fact, we were told, they had no idea how we ever boarded the outbound 3 flights! But, they actually laughed, we were in HKG so obviously something was right. But he said he was sure the others were simply "paying it forward."

And, just to note, in all cases, the Delta staff was friendly as could be. Just a weird happenstance.